The world is filled with ancient monuments built by master craftsmen in order to honor everything from kings and presidents to religious figures. And although most of these landmarks have been carefully studied and researched by scientists and historians, some are simply so old, incomplete, or obscure that we still dont know very much about why they were built or what purpose they served. The following are 10 world landmarks that, whether by intention or simply due to the passage of time, continue to baffle the people who study them.

10. The Cahokia Mounds



Cahokia is the name given to an Indian settlement that exists outside of Collinsville , Illinois . Archeologists estimate that the city was founded sometime around 650 AD, and its complex network of burial grounds and sophisticated landscaping prove that it was once a thriving community. It has been estimated that at its peak the city was home to as many as 40,000 people, which would have made it the most populous settlement in America prior to the arrival of the Europeans. The most notable aspect of Cahokia today are the 80 mounds of earth, some as high as 100 feet, which dot the 2,200-acre site. These helped create a network of plazas throughout the city, and it is believed that important buildings, like the home of the settlements chief, were built on top of them. The site also features a series of wooden posts that archeologists have dubbed woodhenge. The posts are said to mark the solstices and equinoxes, and supposedly figured prominently in the communitys astronomical mythology.

The Mystery
Although scientists are constantly discovering new information about the Cohokia community, the biggest mystery that remains is which modern Indian tribe is descended from the residents of the ancient city, as well as just what it was that caused them to abandon their settlement.

8. The Yonaguni Monument



Of all the famous monuments in Japan , perhaps none is more perplexing than Yonaguni, an underwater rock formation that lies off the coast of the Ryuku Islands . It was discovered in 1987 by a group of divers who were there to observe Hammerhead sharks, and it immediately sparked a huge amount of debate in the Japanese scientific community. The monument is made up of a series of striking rock formations including massive platforms, carved steps, and huge stone pillars that lie at depths of 5-40 meters. There is a triangular formation that has become known as the turtle for its unique shape, as well as a long, straight wall that borders one of the larger platforms. The currents in the area are known for being particularly treacherous, but this has not stopped the Yonaguni monument from becoming one of the most popular diving locations in all of Japan .

The Mystery
The ongoing debate surrounding Yonaguni centers on one key subject: is the monument a natural phenomenon, or is it man-made? Scientists have long argued that millennia of strong currents and erosion have carved the formations out of the ocean floor, and they point to the fact that the monument is all one piece of solid rock as proof that it was not assembled by a builder. Others, though, point to the many straight edges, square corners and 90-degree angles of the formation as proof that its artificial. They often cite one formation in particular, a section of rock that resembles a crude carving of a human face, as evidence. If they are right, then an even more interesting mystery presents itself: who constructed the Yonaguni Monument , and for what purpose?

6. Goseck Circle



One of the most mysterious landmarks in Germany is the Goseck Circle , a monument made out of earth, gravel, and wooden palisades that is regarded as the earliest example of a primitive œsolar observatory. The circle consists of a series of circular ditches surrounded by palisade walls (which have since been reconstructed) that house a raised mound of dirt in the center. The palisades have three openings, or gates, that point southeast, southwest, and north. It is believed that the monument was built around 4900 BC by Neolithic peoples, and that the three openings correspond to the direction from which the sun rises on the winter solstice.

The Mystery
The monuments careful construction has led many scientists to believe that the Goseck Circle was built to serve as some kind of primitive solar or lunar calendar, but its exact use is still a source of debate. Evidence has shown that a so-called œsolar cult was widespread in ancient Europe . This has led to speculation that the Circle was used in some kind of ritual, perhaps even in conjunction with human sacrifice. This hypothesis has yet to be proven, but archeologists have uncovered several human bones, including a headless skeleton, just outside the palisade walls.